Various processes for the preparation of hydrogels are known, both with synthetic products, such as for example polymers and/or resins, and with natural products such as, for example, collagen.
In the particular case of synthetic hydrogels, those currently on the market are carried out, on average, through polimerization and cross-linking (namely, coupling between polymers and monomers) of two or more types of monomers in a random way.
As a main component of the above monomers, acrylamide is very often used. This substance, at a monomer level, is notoriously carcinogenic and, also with the presence of small non-polymerized residues, can create such health problems that in some States its use has been forbidden.
In fact, even if it is possible to subject final hydrogels to an opportune wash, the thick mass of the hydrogel does not allow a homogeneous penetration of the washing solution and, therefore, does not ensure the complete removal of starting monomers and/or oligomers (particularly dimers) which can be formed during the preparation process of the hydrogel.
Finally, it is often not possible to ensure the complete removal of other reagents (for example metals, catalysts, and so on) which usually are employed during the preparation of the hydrogel itself.
Also hydrogels formed through UV rays, gamma rays or with a freeze-thaw system are known, but these procedures give rise to changes of a physical and not chemical nature and for this reason they do not generally ensure any guarantee of stability over time, especially if hydrogels have to be stored in the presence of a high quantity of water, as in the present case.
Furthermore, there exist hydrogels based on raw materials of animal or vegetal origin, whose mean life is however very moderate. Moreover, in case of hydrogels of animal origin, the compatibility of these products with subjects on which one intends to carry out the treatment has generally to be ascertained.
There remains therefore a strong need of being able to provide hydrogels which are: injectable; completely biocompatible and free of residues and/or impurities resulting from their preparation reaction; bioreabsorbable in varying times and reproducible depending on the type of the intended use; having such homogeneity and regularity features in the whole structure that the behaviour towards the organism is advantageous.
The object of the present invention is to provide an adequate answer to the need above pointed out.